Machine And Method For Electrochemically Polishing Indentations Within An Aluminum Wheel

ABSTRACT

A machine for electrochemically polishing indentations within the wall of an aluminum workpiece, such as a wheel, has a cathode attached to an upper platen. The workpiece is mounted upon a lower platen which acts as an anode. Electrolyte is passed between the cathode and the anode while simultaneously a current is applied which passes through the cathode and the anode. The current is selectively pulsed to maximize polishing but at the same time to permit the flushing away of residual material and to cool the cathode and the workpiece.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electrochemical polishing andmore specifically to electrochemically polishing aluminum wheels.

2. Description of Related Art

Electrochemical machining (ECM) is a process for removing material froma metal workpiece to impart a smooth surface which appears to bepolished. Such a process takes place using an electrolyte having a highionic strength. The workpiece to be machined serves as the anode and theelectrode of the electrochemical machining apparatus serves as thecathode. In the polishing process an electric current runs between theanode and the cathode. Under these conditions, the electrode serves as ashaping tool. The workpiece, which serves as the anode, dissolveslocally, for example, in the form of metal hydroxide while hydrogen isformed at the electrode surface. This electrochemical machining methodenables patterns or arbitrarily shaped holes to be formed in a metalworkpiece in a relatively simple and accurate manner. Theelectrochemical machining process may also be used to polish a workpieceby removing less material from the workpiece with the goal of achievinga smoother surface finish, as opposed to purely removing material toproduce a predetermined shape.

However, electrochemically polishing large workpieces requires a largecurrent and in the past, as a result of such a limitation,electrochemical polishing has been limited to relatively small surfaces.Additionally, with a continuous current, material is removed from theworkpiece and the electrolyte always contains residue of the workpiece.

A method and apparatus are needed, whereby a larger workpiece, such as awheel, may be electrochemically polished in an efficient manner thatremoves residue and that results in a superior finish.

SUMMARY OF THE INVENTION

One embodiment of the subject invention is directed to a machine forelectrochemically polishing indentations of known geometry within thewall of an aluminum workpiece, such as a wheel. The workpiece spacedefines the space in which a workpiece would occupy in the machine. Themachine has an upper platen with a cathode extending from the upperplaten, wherein the cathode is associated with an indentation and,wherein the cathode has a shape similar to that of the indentation butsmaller and is adapted to be positioned adjacent to the indentation todefine a gap therebetween for the introduction of an electrolyte betweenthe cathode and the indentation. A lower platen is aligned with theupper platen, wherein the lower platen is adapted to receive the wheeland, wherein the upper platen and the lower platen are movable relativeto one another such that, in a first position, the cathode may bedistanced from the lower platen and, in a second position, the cathodeis close to the lower platen with the cathode adjacent to the locationof the indentation of the workpiece mounted to the lower platen Themachine also has anode shoes for contact with the wheel, wherein theshoes are electrically conductive such that when the shoes contact theworkpieces, the workpiece itself acts as an anode. An entry passagewayintroduces electrolyte within the gap between the cathode and theindentation of the workpiece and an exit passageway removes electrolytefrom the gap between the cathode and the indentation of the workpiece. Apower supply provides current between the cathode of the upper platenand the anode of the lower platen through electrolyte therebetween and acontroller controls the current between the cathode and the anode.

Another embodiment of the subject invention is directed to a method forelectrochemically polishing indentations of known geometry within thewall of an aluminum workpiece. A workpiece space defines the space inwhich the workpiece would occupy in the machine. The method comprisesthe steps of:

-   -   a) mounting an aluminum workpiece upon a platen;    -   b) attaching at least one anode to the workpiece;    -   c) positioning at least one cathode within the indentation        within the workpiece, thereby defining a gap between the cathode        and the anode;    -   d) introducing a flow of electrolyte within the gap;    -   e) introducing a current between the cathode and the anode; and    -   f) pulsing the current to permit the flowing electrolyte to        flush the indentation surface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a front view of a typical wheel that may be polished using themachine and method in accordance with the subject invention;

FIG. 2 is an enlarged section of a portion of the wheel illustrated inFIG. 2;

FIG. 3 is a perspective view of a portion of the top platen with ananode extending therefrom;

FIG. 4 is a sketch of the apparatus in accordance with the subjectinvention;

FIG. 5 is a sketch of the machine illustrated in FIG. 4 but with theupper platen and lower platen adjacent to each other to perform themachining process; and

FIG. 6 is a plan view of a cathode used to polish a closed pocket.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 illustrate details of a typical workpiece, such as a wheel10, which in these figures is an aluminum wheel having a cylindricalprofile defining a wheel rim 15 which supports a tire (not shown) and ahub 20 having a plurality of lug holes 25 extending therethrough forsecuring the wheel 10 with lugs (not shown) extending from the body of avehicle.

The wheel 10 has a plurality of indentations 30 of known geometry withinthe wall 35 of the wheel 10. In particular, an indentation 30 may beeither a window 40 extending through the wall 35 of the wheel 10 or apocket 45 which extends only partially through the wall 35 of the wheel10. It should be appreciated that the electrochemical polishing processassociated with the window 40 is slightly different than the processassociated with the pocket 45. In particular, the electrolyte may beflushed through the window 40 during the process while the electrolytemust be introduced and removed from the pocket 45.

For the electrochemical process to be effective, it is necessary for theanode to conform fairly closely to the shape of the workpiece to bepolished. Directing attention to FIG. 3, the cathode 50 is shaped tohave a substantially similar profile to that of the window 40 (FIG. 2).The cathode 50 must be slightly smaller than the profile of the window40 to create a gap. The gap exists for two reasons. First of all, it isnecessary to introduce an electrolyte within the gap to promote thechemical reaction which removes material from the window 40. Second ofall, the gap must be maintained to prevent electrical arcing between thecathode and the anode since such arcing would pit the walls 42 of thewindow 40. Cathodes 50 are typically made of solid brass.

Briefly turning to FIG. 1 and with respect to FIG. 3, it should beapparent that the cathode 50 may be placed in any one of the windows 40and the locator pin 55 on the upper platen may be placed within the lughole 25 to properly space the cathode 50. The cathode 50 is attached toan upper platen 60. The upper platen 60 has surfaces 65 which contactthe perimeter 43 of the window to vertically position the cathode 50within the window 40.

Directing attention to FIG. 4, a machine 100 is illustrated forelectrochemically polishing indentations 30 such as the window 40 ofknown geometry within the wall 35 of an aluminum wheel 10. A wheel space12 is used to define the volume that would be occupied when an actualwheel 10 is placed within the machine 100. The machine 100 has an upperplaten 60 with two cathodes 50 extending therefrom. Each cathode 50 isassociated with an indentation 30 and each cathode 50 has a shapesimilar to that of the indentation 30, but smaller. Each cathode 50 isadapted to be positioned adjacent to the indentation 30 to define a gaptherebetween, for the introduction of an electrolyte between the cathode50 and the indentation 30.

A lower platen 105 is aligned with the upper platen 60. The lower platen105 is adapted to receive the wheel 10. The upper platen 60 and thelower platen 105 are movable relative to one another such that, in afirst position (FIG. 4), the cathodes 50 may be distant from the lowerplaten 105 and, in a second position (FIG. 5), the cathodes 50 on theupper platen 60 are close to the lower platen 105 and within theindentations 30 of a wheel 10 mounted to the lower platen 105. In FIGS.4 and 5, the indentation 30 is the window 40. This positioning providesa gap 107 through which electrolyte may flow to transmit currenttherebetween.

FIG. 4 illustrates the machine 100 in a first position with the cathodes50 distanced from the lower platen 105. This arrangement is used forset-up so that the wheel 10 may be introduced to or removed from thelower platen 105. The lower platen provides a non-conductive base 110,which may be a glass-filled phenolic material, with locating bolts 112protruding therefrom which engage one or more of the lug holes 25 in thewheel 10. The machine 100 includes anode shoes 115 which contact thewheel 10. The shoes 115 are electrically conductive such that when theshoes 115 contact the wheel 10, the wheel 10 itself acts as an anode.The anode shoes 115 are movable from a first position illustrated inFIG. 4, wherein the shoes 115 are away from the wheel 10 to a secondposition (FIG. 5), wherein the shoes 115 contact the wheel 10. It shouldbe appreciated that in the event the wheel 10 is not mounted within themachine 100, the anode shoes in the second position would be positionedwithin a wheel space 12 identical to the location of the wheel 10.

The anode shoes 115 are attached to linear cylinders 120 capable ofindexing the anode shoes 115 in the first position, as illustrated inFIG. 4, or in the second position, as illustrated in FIG. 5. A powersupply 125 provides current between the cathode 50 of the upper platen60 and the anode 115 of the lower platen 105, but permits such currentto pass between these two parts through the introduction of electrolytetherebetween. The combination of the electrolyte 127 therebetween and acurrent passing between the cathode 50 and the wheel 10, which acts asthe anode through the electrolyte 127, promotes the chemical reactionwhich removes material from the window 40 of the wheel 10. A controller129 controls the current between the cathode 50 and the wheel 10 actingas an anode.

In order to promote the quality of polishing provided by the machine100, the controller 129 further includes a pulsing circuit 131 forallowing the current to be intermittently applied to the cathode 50,thereby permitting the electrolyte 127 to more effectively flush residuefrom the wheel 10. The controller 129 provides at least a machining modeand a polishing mode. In the machining mode, the current is high toremove a substantial amount of material from the wheel 10. In thepolishing mode, the current is lower to remove a substantially lessamount of material from the wheel 10. As a result, a wheel 10 with arelatively rough finish may first be “machined” and then “polished” toproduce a finished product. With such a two-stop process, it may bepossible to eliminate a preliminary mechanical grinding step whichheretofore preceded the electrochemical machining process.

While the parameters for pulsing the current used for this process isdependent upon a variety of factors such as workpiece size, the gapbetween the cathode and the workpiece and the composition of theelectrolyte, in general, the pulsing of the current for the machiningmode is approximately 50 milliseconds on and 25 milliseconds off for atypical workpiece. For the polishing mode, the pulsing of the current isapproximately 40 milliseconds on and 20 milliseconds off. Overall, thecurrent may be pulsed at a rate of between 20-25 milliseconds on and8-30 milliseconds off. The inventors have discovered that the pulsingprocess itself greatly improves the efficiency of the polishing processand that this two stage machining/polishing method further enhances theeffectiveness of the pulsing process.

Additionally, as a general guideline for a typical workpiece, thecurrent may be between 12,000-15,000 amperes and the voltage may bebetween approximately 0-25 volts direct current.

It should be appreciated that a flow of electrolyte 127 is necessary fornormal operation of the machine 100. The flow of electrolyte 127 notonly promotes the transfer of current between the anode and the wheel10, but furthermore, provides a mechanism for removing heat and residuefrom the working region of the wheel 10.

Directing attention to FIG. 4, from a reservoir 135 electrolyte 127 isdelivered through a pump 138 through a conduit 140 to an entrypassageway 143, which in FIG. 4 is a sleeve 145 surrounding each cathode50 so that the electrolyte 127 may be introduced around the perimeter ofthe cathode 50. FIG. 3 further illustrates that this sleeve 145 extendsthrough the upper platen 60 and surrounds the cathode 50. It should benoted in FIG. 3 that a seal 147 surrounds the sleeve 145. The seal 147is comprised of a flexible nonporous material surrounding the cathode 50and entry passageway 143. While the sleeve 145 is illustrated as themechanism for dispersing the electrolyte 127 about the perimeter of thecathode 50, this sleeve 145 may in the alternative be a plurality ofports about the perimeter of the cathode 50 to achieve the same result.The entry passageway 143 conforms to the perimeter of the cathode 50 andwhen a cathode 50 having a different geometry is used, the associatedentry passageway 143 again conforms to the perimeter of the new cathode50.

Directing attention to FIG. 5, when the upper platen 60 is positionedagainst the wheel 10, the seal 147 is urged against the wheel 10 therebyproviding a watertight seal between the upper platen 60 the wheel 10 tocontain the electrolyte 127. Examining both FIGS. 4 and 5, theelectrolyte 127 travels through the sleeve 145 around the cathode 50 andthrough an exit passageway 150 which in FIG. 4 is the window 40 of thewheel 10. In this arrangement, the electrolyte 127 may be drainedthrough the window 40 into a collection tank 153 where it is thenreturned to the reservoir 135 to be used again. As illustrated in FIG.4, the electrolyte 127 in the reservoir 135 is diverted to a reclamationstation 155 to remove impurities from the electrolyte 127 that wereintroduced during the polishing process. One reclamation techniqueinvolves the introduction of iron nitrate with the spent electrolyteafter which time the fluid is centrifuged. This technique is betterdescribed in a co-pending U.S. patent application Ser. No. 11/465,839titled “Process For Regenerating Electrolytes In ElectrochemicalPolishing Applications” filed Aug. 21, 2006 and assigned to the sameassignee as the present application. It should also be noted in FIG. 4that the wheel 10 rests upon the collector tank 153, such that the wheel10 provides a seal against the tank 153 to minimize the loss ofelectrolyte.

The cathodes 50 of the subject invention are customized to act upon thewindow 40 of the wheel 10, illustrated in FIGS. 1 and 2. It should beappreciated that each cathode 50 is removable and may be replaced with adifferently shaped cathode to accommodate indentations of differentshapes on wheels. FIGS. 3, 4 and 5 illustrate the cathode 50, which isremovably attached to the upper platen 60. The upper platen 60 isslideably mounted upon posts 160 so that it may be moved between thefirst position, wherein the upper platen 60 is spaced from the wheel 10(FIG. 4), then to the second position, wherein the upper platen 60 isadjacent to the wheel 10 (FIG. 5). It should also be appreciated thatthe upper platen 60 and the lower platen 105 are electrically insulatedfrom the anode, which is the wheel 10, and from the cathodes 50.

From inspection of FIG. 1, it is apparent that there are multiplewindows 40 within a wheel 10. In one embodiment of the subjectinvention, two windows 40 are polished simultaneously although a singlewindow may also be polished. The subject invention is also designed toindex the wheel 10 or another workpiece so that different windows can bepolished by the same cathode. However, because the electrochemicalpolishing process requires a high current, prior art designs forelectrochemical polishing use a single cathode. Additionally, the lowerplaten 105 is indexable such that wheel 10 having multiple indentations30 may be rotated to align different indentations 30 with the cathodes50 for polishing. In particular, a CNC controlled servo-drive motor 163drives a pulley 165 which drives a belt 167 to rotate a second pulley170 which rotates a shaft 172, thereby rotating the lower platen 105 andthe wheel 10 attached thereto. By doing so, it is possible to index thewheel 10 so that different windows 40 are aligned with the cathodes 50for polishing. As a result, polishing the eight windows 40 in the wheel10, illustrated in FIG. 1, requires indexing the wheel 10 only fourtimes as opposed to indexing the wheel 10 eight times when there is asingle cathode 50 operating upon a window 40.

The electrolyte 127 is comprised of a solution of sodium nitrate (NaNO₃)and water. The flow of electrolyte 127 for a typical application may bebetween 25-55 gallons per minute. As a particular example, for a wheel10 having a diameter of 20 inches and indentations 30 proportional tothat size, the flow of electrolyte may be between 45-50 gallons perminute. For a wheel 10 having a diameter of 18 inches and indentations30 proportional to that size, the flow of electrolyte may be between30-35 gallons per minute. The gap 107 between the cathode 50 and thewall 35 of the window 40 is typically about 0.75 millimeters, however,in regions where a greater degree of polishing is required during theoperation, this gap may be slightly smaller, keeping in mind that a gapthat is too small will result in undesirable arcing between the cathode50 and the anode, which is the wheel 10.

With the electrolyte 127 flowing around the cathodes 50, the pulsingcircuit 131 of the controller 129 is capable of turning the current onand off so that the electrolyte has a chance not only to cool the wheel10, but furthermore, to wash away any impurities it may have accumulatedon the wall 35 of the window 40 in the wheel 10.

So far the discussion has been directed to electrochemically polishing awindow 40 within a wheel 10. As illustrated in FIGS. 1 and 2, theindentation 30 may also be a pocket 45 which does not extend through thewall 135 of the wheel 10. As a result, for polishing a pocket 45, theelectrolyte 127 must be directed in a different fashion. FIG. 6illustrates the upper platen 60 having a cathode 180 extendingtherefrom. A seal 182 surrounds the cathode 180 to provide a water-tightseal when the upper platen 60 is placed over the pocket 45. The purposeof this design is to deliver electrolyte 127 over the sides and the faceof the cathode 180. In particular, an entry passageway 185 on one sideof the cathode 180 introduces the electrolyte 127 to what is now anenclosed chamber 187. The electrolyte 127 flows across the cathode 180and is removed from the chamber 187 through an exit passageway 189 wherethe electrolyte is then delivered to the collection tank 153,illustrated in FIG. 4. With respect to the wheel 10 illustrated in FIG.1, the upper platen 60 illustrated in FIG. 6, has two locating pins 190(FIG. 6), which fit within the lug holes 25 adjacent to the pocket 45 tobe polished.

The subject invention is also directed to a method for electrochemicallypolishing indentations 30 of known geometry within the wall 35 of analuminum wheel 10. A wheel space defines the space in which a wheel 10would occupy in the machine 100. The method is comprised of the steps ofmounting an aluminum wheel 10 upon a platen 105 and attaching at leastone anode through, for example, anode shoe 115 to the wheel 10. At leastone cathode 50 is positioned within the indentation 30 of the wheel 10,thereby defining a gap 107 between the cathode 50 and the anode. Anelectrolyte 127 is introduced within the gap and a current is thenintroduced between the cathode 50 and the anode. The current is pulsatedto permit the flowing electrolyte 127 to flush impurities from thesurface of the indentation 30. The electrolyte is recirculated duringthe polishing process, but furthermore, the electrolyte is reclaimedthrough a reclamation process, such as that process previously describedherein.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. The presentlypreferred embodiments described herein are meant to be illustrative onlyand not limiting as to the scope of the invention which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

1. A machine for electrochemically polishing indentations of knowngeometry within the wall of an aluminum workpiece, wherein a workpiecespace defines the space in which a workpiece would occupy in the machineand wherein the machine comprises: a) an upper platen; b) a cathodeextending from the upper platen, wherein the cathode is associated withan indentation and wherein the cathode has a shape similar to that ofthe indentation but smaller and is adapted to be positioned adjacent tothe indentation to define a gap therebetween for the introduction of anelectrolyte between the cathode and the indentation; c) a lower platenaligned with the upper platen, wherein the lower platen is adapted toreceive the workpiece and wherein the upper platen and the lower platenare movable relative to one another such that in a first position thecathodes may be distanced from the lower platen and in a second positionthe cathode is close to the lower platen with the cathode adjacent tothe location of the indentation of a workpiece mounted to the lowerplaten; d) anode shoes for contact with the workpiece, wherein the shoesare electrically conductive such that when the shoes contact theworkpieces, the workpiece itself acts as an anode; e) an entrypassageway to introduce electrolyte within the gap between the cathodeand the indentation of the workpiece; f) an exit passageway to removeelectrolyte from the gap between the cathode and the indentation of theworkpiece; g) a power supply to provide current between the cathode ofthe upper platen and the anode of the lower platen through theelectrolyte therebetween; and h) a controller for controlling thecurrent between the cathode and the anode.
 2. The machine according toclaim 1, wherein the workpiece is a wheel.
 3. The machine according toclaim 1, wherein at least two cathodes extend from the upper platen,wherein each cathode is associated with an indentation, wherein eachcathode has a shape similar to that of the indentation but smaller andis adapted to be positioned adjacent to the indentation to define a gaptherebetween for the introduction of an electrolyte between the cathodeand the indentation, and wherein the upper platen and the lower platenare movable relative to one another such that in a first position thecathodes may be distanced from the lower platen and in a second positionthe cathodes are close to the lower platen with the cathodes adjacent tothe locations of the indentation of a workpiece mounted to the lowerplaten.
 4. The machine according to claim 1, wherein the controllerfurther includes a pulsing circuit for allowing the current to beintermittently applied to the cathode thereby permitting the electrolyteto more effectively flush residue from the anode.
 5. The machineaccording to claim 4, wherein the controller has at least a machiningmode and a polishing mode, and wherein in the machining mode, thecurrent is high to remove a substantial amount of material from theworkpiece while, in a polishing mode, the current is lower to remove asubstantially less amount of material from the workpiece
 6. The machineaccording to claim 1, wherein the indentation is a window extendingthrough the wall of the workpiece, the entry passageway surrounds thecathode so that the electrolyte may be introduced around the perimeterof the cathode, and the exit passageway is the window so that theelectrolyte may be drained through the window.
 7. The machine accordingto claim 6, wherein the passageway is a series of ports about theperimeter of the cathode.
 8. The machine according to claim 6, whereinthe passageway is a sleeve about the perimeter of the cathode.
 9. Themachine according to claim 1, wherein the indentation is a pocket in thewall of the workpiece, the entry passageway is a slot on one side of thepocket and the exit passageway is a slot on the opposite side of thepocket such that electrolyte may be introduced within the gap from oneside of the pocket and discharged from the opposing side of the pocket.10. The machine according to claim 1, wherein the cathode is removablyattached to the upper platen so that different cathodes may be installedto accommodate indentations of different shapes.
 11. The machineaccording to claim 1, wherein the upper platen is slidably mounted formoving between the first position and the second position.
 12. Themachine according to claim 1, wherein the upper platen and the lowerplaten are electrically insulated from the anodes and the cathodesattached thereto.
 13. The machine according to claim 1, furtherincluding flexible non-porous material surrounding each cathode andentry passageway, wherein the material is adapted to mate against theworkpiece to provide a water-tight seal between the upper platen and theworkpiece.
 14. The machine according to claim 1, wherein the anode shoesare movable from a first position away from the workpiece space to asecond position within the workpiece space such that the shoes wouldcontact a workpiece mounted within the workpiece space.
 15. The machineaccording to claim 1, wherein the lower platen is indexable such that aworkpiece having multiple indentations may be rotated to align differentindentations with the cathode.
 16. The machine according to claim 1,further including a collector tank for collecting electrolyte after ithas passed through the gap between the cathode and the anode.
 17. Amethod for electrochemically polishing indentations of known geometrywithin the wall of an aluminum workpiece, wherein a workpiece spacedefines the space in which a workpiece would occupy in the machine andwherein the method comprises the steps of: a) mounting an aluminumworkpiece upon a platen; b) attaching at least one anode to theworkpiece; c) positioning at least one cathode within an indentation ofthe workpiece, thereby defining a gap between the cathode and the anode;d) introducing a flow of electrolyte within the gap; e) introducing acurrent between the cathode and the anode; and f) pulsing the current topermit the flowing electrolyte to flush the indentation surface.
 18. Themethod according to claim 17, wherein the workpiece is a wheel.
 19. Themethod according to claim 17, wherein the step of pulsing the current isa two step process in which in a machining step the current is greaterto remove a substantial amount of material while in a subsequentpolishing step the current is less to remove a substantially less amountof material.
 20. The method according to claim 19, wherein the currentfor the machining step is approximately 50 milliseconds on and 25milliseconds off.
 21. The method according to claim 19, wherein thecurrent for the polishing step is approximately 40 milliseconds on and20 milliseconds off.
 22. The method according to claim 17, wherein thecurrent is between approximately 12,000 and 15,000 amperes and thevoltage is between approximately 0 and 25 volts direct current.
 23. Themethod according to claim 17, wherein the current is pulsed at a rate ofbetween approximately 20-25 milliseconds on and between approximately8-30 milliseconds off.
 24. The method according to claim 17, wherein theflow of electrolyte is in the range of 25-55 gallons per minute.
 25. Themethod according to claim 18, wherein for a wheel having a diameter of20 inches, the flow rate is between 45-50 gallons per minute.
 26. Themethod according to claim 18, wherein for a wheel having a diameter of18 inches, the flow rate is between 30-35 gallons per minute.
 27. Themethod according to claim 17, wherein the electrolyte is recirculated toprovide electrolyte within the gap.
 28. The method according to claim17, wherein the electrolyte is filtered to remove residue beforerecirculation.
 30. A method for electrochemically polishing indentationsof known geometry within the wall of an aluminum workpiece, wherein aworkpiece space defines the space in which a workpiece would occupy inthe machine and wherein the method comprises the steps of: a) mountingan aluminum workpiece upon a platen; b) attaching at least one anode tothe workpiece; c) positioning at least one cathode within theindentation within the workpiece, thereby defining a gap between thecathode and the anode; d) introducing a flow of electrolyte within thegap; and e) introducing a pulsing current between the cathode and theanode, wherein the current is on for a predetermined period to polishthe workpiece indentation and then off for a predetermined shorterperiod to permit the flowing electrolyte to flush the indentationsurface.